The invention relates to a method of positioning a patient arranged on the top of a patient table, where a first X-ray image is formed with the central ray extending in a first direction, which image is electronically stored. The table top is then displaced in a first direction and a second direction which is perpendicular thereto during a first positioning operation, the X-ray image and an electronic marker superposed thereon being shifted relative to one another on a monitor in accordance with the path of travel. The invention also relates to an apparatus for performing the method.
For many examinations and treatments in the medical field it is necessary to bring a given region of a patient in an exactly defined position. For example, for the crushing of renal calculi the patient must be moved in space so that the concrement, i.e. the renal calculus, is positioned exactly in the focus of a shock-wave generator for crushing concrements.
It is known that in apparatus of this kind the location and positioning can be performed by means of an X-ray fluoroscopy device. The table top is then displaced under fluoroscopic control from different perspectives until the image of the renal calculus is situated in a given position within the fluoroscopic image, for example in the center of the image, the position being made visible preferably by means of a suitable electronic marker, for example by means of cross-hairs. It is a drawback that during such a positioning operation not only the patient but also the operator is exposed to a comparatively large radiation dose, because fluoroscopy is continued until the renal calculus is situated in the desired position.
In the method and apparatus described in the preamble, being known from EP-OS 160 583, the radiation dose is reduced because positioning is performed by means of a single X-ray image for which the X-rays need only be briefly switched on. However, accurate positioning can then be realized only if the concrement happens to be already present in the plane parallel to the table top in which its desired position is situated. Otherwise accurate position is not possible, that is to say not in the longitudinal and the transverse direction of the table top either, because an X-ray image is a central projection.